What Is Point-to-Point Tunneling Protocol (PPTP)?
The Point-to-Point Tunneling Protocol (PPTP) is a method for implementing virtual private networks. PPTP service uses a control channel over TCP and a GRE tunnel operating to encapsulate PPP packets.
The PPTP service specification does not describe encryption or authentication features and relies on the Point-to-Point Protocol being tunneled to implement security functionality. However, the most common PPTP implementation, shipping with the Microsoft Windows product families, implement various levels of authentication and encryption natively as standard features of the Windows PPTP stack. The intended use of this protocol is to provide security levels and remote access levels comparable to typical VPN products.